Installation: identify RPi platform

[jmtayloruk]

Since I haven't worked out how to do optional extras as part of a pip install, it would be very useful to be able to identify reliably when the installation is taking place on a Pi. That would enable us to install picamera etc automatically as part of the pip install, but only on the Pi.

The various available platform-related keys are listed here: https://www.python.org/dev/peps/pep-0508/#environment-markers . However, it sounds like there may not be any that uniquely identify something as a Pi. [I’m not sure if there’s a way of specifying that the marker contains a string, rather than matches a string, but that condition might prove useful, I suspect].

Chas says: from past experience, platform_machine should report armv7 (or whatever). JT: but that does not distinguish the Pi from other embedded platforms, and I would like to be able to use e.g. Odroid as well.

Chas also says: try https://gist.github.com/barseghyanartur/94dbda2ad6f8937d6c307811ad51469a - we may need to update the 'value not in' list. JT: but that is a python script - can it be used in any way from pyproject.toml?? Or I suppose perhaps we could do it from a setup.py script, if it's not considered old-fashioned to also have code in that...